1. Field of the Invention
The invention relates in general to a backlight module and a liquid crystal display (LCD) device incorporating the same, and more particularly to a backlight module and a liquid crystal display (LCD) device incorporating the same capable of reducing the leakage current between the light source and the frame.
2. Description of the Related Art
Along with the advance in the manufacturing technology of liquid crystal display (LCD) device devices and further due to the features of slimness, lightweight, low energy consumption and no radiation, LCD devices have been widely applied in various electronic products such as personal digital assistant (PDA), notebook computer, digital camera, digital video recorder, mobile phone, computer monitor, and liquid crystal TV. And further with large amount of input in research and development and the adoption of large-scaled production facilities, the quality of LCD devices continue to increase yet the prices keep falling down. Consequently, the application of LCD devices grows wider and wider. However, the LCD panel of an LCD device is a not a self-luminous display panel, and can not display without being availed by the light provided by a backlight module.
The backlight module can be categorized into side-type backlight module and direct-type backlight module according to the position of the light source in the backlight module. In the side-type backlight module, the cold cathode fluorescent lamp (CCFL) is disposed in a lateral side of the LCD panel. The light emitted by the CCFL is transmitted towards a light guide plate disposed at the rear of the LCD panel, so that the incident light is spread by the light guide plate.
Conventional direct-type backlight module includes a frame, a reflector, a number of CCFLs, a diffuser and an optical film. An accommodation recess is formed on the top surface of the frame. The reflector is disposed on the bottom and the wall of the accommodation recess. The CCFLs are arranged in the accommodation recess and positioned above the reflector. The diffuser is disposed above the CCFLs. The optical film module is disposed above the diffuser. The optical film includes a prism, a diffuser or a brightness enhancement film. When assembled with the direct-type backlight module, the LCD panel is disposed above the optical film.
The conventional direct-type backlight module is exemplified by the two-terminal driven mode. The lamp inverter needs to apply a high voltage to the electrode terminal at the two ends of the lamp, so that an expected lamp current is provided for the lamp to illuminate. For example, the lamp inverter respectively provides +1 kv and −1 kv to the two electrode terminals of the lamp. Therefore, the light emitted by the lamp is directly projected onto the LCD panel after having subsequently gone through the optical processing of the reflective plate, the diffuser, and the optical film.
However, the frame is normally a metal conductor, so parasitic capacitance or stray capacitance would occur between the electrode terminal of the lamp and the frame when a high voltage is applied to the lamp. Part of the lamp current provided to the lamp by the lamp inverter would be leaked to the frame, resulting in the so-called “leakage current” and reducing the luminance efficiency of the backlight module. Since the lamp current received by the lamp is smaller than the expected lamp current, so the luminance efficiency of the lamp will be weakened. Thus, the luminance quality of the backlight module is severely affected, largely reducing the practicality of the LCD device.